Alpha-sulfo branched chain fatty acids and method for preparing them



United States Patent Ofiice 3,408,373 Patented Oct. 29, 1968 ABSTRACT OF THE DISCLOSURE Branched chain fatty acids of the formula RCH(R')CO H where the sum of the carbon atoms of R and R is between and were prepared by the peroxide-initiated free radical addition of normal fatty acids in linear a-olefins. Sulfonation with dioxane-SO and neutralization, gave surface-active salts of oc-SUlfO branched chain fatty acids with excellent wetting properties.

A non-exclusive, irrevocable, royalty-free license in the invention hereindescribed, throughout the world for all purposes or" the United States Government, with the power to grant sublicenses for such purposes, is hereby granted to the Government of the United States of America.

This invention relates to compounds with surface ac tive properties, and particularly relates to 2-sulfo-2-alkyl carboxylates and a method for their preparation.

An object of the present invention is to provide novel detengents and wetting agents. Another object is to prepare oc-SlllfO derivatives of Z-alkyl carboxylic acids. A [further object is to provide surface active agents of improved water solubility. Further objects and a fuller understanding of the invention may be had by referring to the following description and claims.

Although some 2-alky1 carboxylic acids have previously been prepared, the a-sulfonated derivatives are not available because the usual methods of sulfonation have not been found applicable. We have discovered, however, that the sulfonate group may be introduced into 2-alkyl carboxylic acids by employing a system containing at least about 50% excess 50;, in the presence of dioxane.

According to the present invention a 2-alkyl carboxylic acid of the formula RCH(R')COOH wherein R is a straight chain alkyl radical having 7 to 16 carbon atoms, R is a straight chain alkyl radical having 1 to 10 carbon atoms and the sum of the carbon atoms of R+R' is an integer from 10 to 20, is prepared by the free radical addition of a straight chain monocarboxylic fatty acid having from 4 to 18 acrbon atoms and a terminal olefin of the formula CH (CH ,CH=CH wherein n is an integer from 1 to 15, by heating the presence of an initiator such as t-butyl peroxide, the 2-alky1 carboxylic acid is separated from the reaction mixture and combined with at least about 50% molar excess each of S0 and dioxane in an inert solvent, such as carbon tetrachloride, and slowly heated to about 60 C. to produce an a-sulfonated compound of the formula RC (R) (SO H) C'OOH wherein R and R are as previously described.

The thermal decomposition of alkyl peroxides such as t-butyl peroxide in the presence of a carboxylic acid removes an a-hydrogen from the acid and produces a free carboxylic acid radical. The free radical will add to a terminal olefin forming a free dialkylacetic acid radical which can abstract an a-hydrogen atom from a second molecule of carboxylic acid. This chain sequence leads to 60-70% yield of 2-alkyl carboxylic acids.

!Many of the Z-alkyl carboxylic acids can be prepared in two specific ways, that is, employing two dilferent combinations of starting materials.

To illustrate:

CH3(CH2)CH2COOH CH3(CH2)13CH=OH;

hexanoic acid hexadecene 7 2-butyl steal-i0 acid CH (OH OI-I C OOH CH CH2CH=CHz stearic acid butane-1 In each addition reaction the product is 2-butyl stearic acid. Referring to the formula RCH(R')COOH, it is thus apparent that the alkyl radicals, R and R, may be derived from either reactant.

In a typical preparation of a 2-alkyl carboxylic acid, a carboxylic acid, an olefin and t-butyl peroxide are combined in a molar ratio of 102110.25, respectively. Twothirds of the acid to be used is placed in an appropriate size flask equipped with condenser, stirrer, dropping funnel and thermometer. The remaining one-third of acid is mixed with the olefin and peroxide. After heating the acid to reaction temperature to 160 C.), the acid-olefin-peroxide mixture is added dropwise over a six-hour period with stirring. After complete addition, the mixture is maintained for an additional hour at reaction temperature. The Z-alkyl carboxylic acid product is isolated by vacuum distillation.

The olefins and aliphatic carboxylic acids were distilled prior to use, the center cut of the distillate being separated and its characteristics compared with literature values.

Example 1 Propionic acid, 740 g. (10 moles) octadecene-1-, 250 g. (1.0 mole) and 36.5 g. (0.25 mole) t-butyl peroxide were measured, and two-thirds of the acid was placed in a four-neck, round-bottom flask. The acid in the flask was heated to C. and this temperature maintained while the remaining acid, the olefin and the peroxide were combined and added dropwise to the flask. As previously described, total time for reaction was seven hours. Simple distillation at reduced pressure provided a crude fraction of product which was purified by distillation through a 24- inch spinning band column. The product, 2-methyleicosenoic acid, collected at 1724 C. at 0.20 mm. mercury pressure, was obtained in 57% yield and had a melting point of 6061 C. Carbon-hydrogen and neutral equivalent analysis indicated a purity of. over 98%.

Example 2 The procedure of Example 1 was repeated except that the olefin used was hexadecene-l (222 g.), and the product was Z-methyloctadecanoic acid.

Example 3 In a manner similar to that of Example 1, two-thirds of 500 g. of hexanoic acid was placed in the flash and heated to about C. The remainder of the hexanoic acid, 72.6 g. of dodecene-l, and 15.8 g. of t-buty-l peroxide were combined and added dropwise. Following the reaction, Z-butyltetradecanoic acid was recovered by distillation in 63% yield.

Examples 4-6 Procedures employed were substantially that of Example 1. The reactants employed and some physical and chemical properties of the products of these examples and 3 4 data pertaining to Examples 1-3 are summarized in the preparation of the 2-sulfonated derivatives were puri- Table I. fied prior to combining for the reaction. Reagent grade Sulfonation reactions conducted with too great an ex carbon tetrachloride was passed through a 12-inch colcess of sulfur trioxide, or under too high a temperature, umn of silica gel and stored over anhydrous sodium sulresult in charring and side-product formation and the imfate until used. Dioxane was distilled through a 24-inch purities interfere with separation of the product desired vacuum jacketed column filled with protruded packing.

TABLE I.DATA REGARDING PREPARATION AND PROPERTIES OF SOME 2-ALKYL CARBOXYLIC ACIDS Example Reaetants Reaction a Yield, M.P., B.P., b Neut. Equival.

Number Temp, C. Acid Product percent 0. C./m.m.

Olefin Acid Found Theory 1 Oetadecene-l Propionie 140 Z-methyleicosanoic 57 60-1 172-4/0. 20 331 326 2 Hexadecene-l do 138 Z-methyloctadecanoic 56 54-5 164-8/0. 20 305 298 160 Z-butyltetradeeanoic 63 26 152-3/0. 30 282 284 160 2-heptylundecanoic 60 18-9 151/0. 30 283 284 160 2-octyldecanoie 68 33-4 1623/0.05 287 284 1sobutyric 145 2,2-dimethylhexadecanoie 36 465-75 114-6/0.20 287 284 Reaction temperatures are indicated as the median of a 36 range. b All melting points and boiling points are uncorrected The use of a sulfur trioxide-dioxane adduct in carbon The center cut of the dioxane distillate was separated,

tetrachloride makes it possible to conduct the sulfonation passed through a 12-inch column of silica gel and stored with only about a 50% molar excess of S0 The use of over anhydrous sodium sulfate. The sulfur trioxide was a higher ratio of SO -dioxane, such as IOU-150% molar freshly distilled prior to use.

excess, appeared to have no advantage. Example 7 The reactants are combined at room temperature and, after the reaction is well initiated, the reaction mixture 'y Carbon tetrachloride, 240 and 16 gis heated to above about 0, preferably in the range mole) y diOXaIle were Combined i u d t m fl sk of about 60 c., to complete the sulfonation with a q pp with a bar g condenser and drying tubeminimum of discoloration and by-product formation. The mixture Was stirred Whil? f to 15 al1d After a total of about two hours heating the reaction mix- 30 mole) of ly dlstllled sulfur tl'lfiXide 1 1 30 ture is only a light amber color, the solvents are removed Of carbon tstl'achlorlde Was added, formmg a whim, by distillation under vacuum, and the 2-sulfo derivative crystalline Y- After stirring the sulfur tfioxide-dioxafle is readily separated and purified as the disodium salt. y for 10 minutes, 30 mole) of y The amount of dioxane added is preferably a molar elcosanoic acid (Pllrified Product of Example in 30 ratio at least equal to that of the sulfur trioxide. In prac- 3 of carbon tetrachloride Was added- T ixtu was tice a small excess, 5l0%, of dioxane was used to insure stirred at room temperature 15 minlltfis, for favorabl reaction conditions. 45 minutes and 60 C. for an additional hour. The reaction mixture was filtered to remove insolnbles and vola- The sulfonated derivative may be obtained as the free f1 t d f h fil acid, as a mono-alkali salt of sodium, potassium or am- 1 were evaPora e .romt 6 Hate under vacuum The residue was dissolved 1n 250 ml. absolute ethanol and neu- I u n o 25:23.33:5531 53233 512.33332:133:21; a a droxide, Potassium hydroxide or ammonium hydroxide, product, disodlum 2-sulfo-2-methyle1c0sanoate, precipitatis considered to neutralize the SO H group first, and at was collected m a filter funnel and recrystalhzed twlce a certain pH, such as about 4.5, or by adding a calculated from ethanol-water mlxture' amount of alkali, a compound of the formula 45 Examples 8-11 RC(R) (SO M)COOH In a manner similar to that described in Example 7,

disodium 2-sulfo-2-alkyl carboxylates were prepared from the 2-alkyl carboxylic acids of Examples 2 to 5. Analytical data for the compounds of Examples 7 t where M is sodium, potassium or ammonium, is obtained and R and R are previously described. Complete neutr l' to a rza 1 11 gives a compound of the formula 11 is presented m Table IL B The disodium salts were readily separated and purified; where M and M are sodium, potassium or ammonium or hence, are a Conveniently P p derivative and at the mixtures thereof. The 2-sulfo-2-alkyl carboxylic acids are same time Practical derivative for use as a surface active agent. Attempts to sulfonate 2,2-dimethylhexadecanoic acid resulted in the formation of a complex mixture of RC(R) (SO M)COOR products.

H u Monosodium salts (soa s) of the com ounds of Examwhere R is preferably a short carbon chain alkyl gro p ples 1 to 6 were prepared by neutralizirfg the acids with such as 1 to 6 carbon atoms by refluxing with a selected sodium hydroxide and recovering the salts. Pertinent suralcohol employing azeotrop1c removal of water. face active properties of these sodium salts and of the In order to provide conditions conducive to obtaining disodium salts of the 2-sulfonated derivatives (Examples optimum yields of product, the solvents and reagents for 711) were determined and are summarized in Table III.

also converted to alkyl esters of the formula TABLE II.ANA.LYSIS OF DISODIUM Z-SULFO-Z-ALKYL CARBOXYLATES RRC(C02NA SO3N8 Anal sis Example Substituents y Number Compound Found Theory C H S Na 0 H S Na Disozdiumhzlsuliot H3 me y eicosanoa e C C15H31 55. 74 9.22 6.53 9. 89 56.00 2-methyloctadecanoate CH3 C1aH33 54.03 10 2-butyltetradeeanoate- C C12H25 53. 40 8.40 8.30 11.28 52. 94 8.33 7.84 11:27 Z-heptylundecanoate 01H. C Hw 52.68 8. 28 7.57 11.40 52. 94 8.33 7. 84 11.27 52. 12 8. 26 8. 08 ll. 58 52. 04 8. 33 7. 84 11. 27

Z-oetyldecauoate 051.111 Gall" TABLE TIL-SOME SURFACE ACTIVE PROPE RTIES OF SODIUM SALTS F Z-ALKYL CAR- B OXYLIC ACIDS AND 2-SULFONATED DERIVATIVES Krafit Surface Micelle Wetting Deter- Foam Salt Point, 'Iensior, Cone. Time, gency e Height,

C. Dynes/ 25 0., Sec. Reflecmm.

cm. Percent tance Monosodium Octadecanoate (sodium stearate) 67. 0.015 300 35 238 2-methylelcosanoate 55.8 35. 1 0. 18 300 30 149 2-methyloctadecanoate. 40. 5 26. 1 0.29 300 29 217 2-butyltetradecanoate. 1 28. 9 0. 07 48 21 210/ 130 2-heptylundecanoate 12 31. 6 0.15 300 20 210/15 loctyldecanoate 17 31. 6 0. 13 100 18 230/45 2,2-dimethylhexadecanoate 39 26. 0 0. 04 86 25 215 Disodium 2-sulfoactadecanoate 92 0. 10 20 2-sulfo-2-methylelcosanoate 53 41. 4 0. 01 300 22 193 2-sulfo2-methyloctadecanoate 43. 5 33. 8 0. 04 49 22 200 2-sulfo2-butyltetrodecanoate 32. 5 36. 7 0. 28 7. 4 8 85/5 2-sulfo-2'heptylundecanoate 55. 5 34. 8 0.37 4. 8 8 0 2 sulfo-2-octyldecanoate 67 35. 5 5. 0 8 0 Temperature at which a 1% dispersion becomes a clear solution on gradual heating.

0.1% concentration, C. with DuNouy tensiometer. 0 Critical micelle concentration determined by pinaeyanole method.

0.1% solutions in distilled water at 25 C. with a 5 g. cotton skein and a 3 g. hook.

5 minutes.

The Krafft point is indicative of solubility of the compound in water, the lower the value the greater the solubility. Comparing several monosodium salts with a total of eighteen carbon atoms, the branched chain soaps such as Z-butyltetradecanoate, 2-heptylun-decanoate, and 2- octyldecanoate have Kratft points of 1, 12 and 17 C., respectively, as compared to 67.5" C. for sodium stearate. These soaps have fairly good detcrgency and good initial foaming properties in soft water, so their solubility makes them particularly suitable for use in liquid detergents.

The disodium salts of the Z-sulfonated derivatives of 2-alkyl carboxylic acids are also more soluble in soft water than corresponding straight carbon chain compounds.

The foregoing is presented to illustrate the invention and is not intended to be in limitation thereof.

We claim:

1. A compound of the formula wherein R is a straight carbon chain alkyl having 7 to 16 carbon atoms, R is a straight carbon chain alkyl having 1 to 10 carbon atoms and the sum of carbon atoms of R+R is an integer from 10 to 20, M is selected from the group consisting of hydrogen, sodium, potassium, and ammonium; and M is selected from the group consisting of hydrogen, sodium, potassium, ammonium and an alkyl having 1 to 6 carbon atoms.

2. A compound of the formula of claim 1 wherein M and M are hydrogen.

2-sulfo-2-methylcicosanoic acid. 2-sulfo-2-methyloctadecanoic acid. 2-sulfo-2-butyltetradecanoic acid. 2-sulfo-2-hepty1undecanoic acid. Z-sulfo-Z-octyldecanoic acid. A compound of the formula of claim 1 wherein M and M are sodium.

9. Disodium 2-sulfo-2-methyleicosanoate.

10. Disodium 2-sulfo-2-methyloctadecanoate.

11. Disodium 2-sulfo-2-buty1tetradecanoate.

12. Disodium 2-sulfo-2-heptylundecanoate.

13. Disodium Z-sulfo-Z-octyldecanoate.

B gneease in reflectance after washing G.D.C. #26 standard soiled cotton in 0.25% solutions in distilled water 0.25% solutions in distilled water by the Boss-Miles test at 60 C. The ratios indicate foam degeneration after 14. A process for preparing 2-sulfo-2-alkylcarboxylic acids of the formula s o H wherein R is a straight carbon chain alkyl having 7 to 16 carbon atoms, R is a straight carbon chain alkyl having 1 to 10 carbon atoms, and the sum of the carbon atoms of R-l-R'is an integer from 10 to 20, said process comprising mixing a 2-alkylcarboxylic acid of the formula wherein R and R have the same meaning as above, with at least about a molar excess of S0 and dioxane in an inert solvent at room temperature, and heating the mixture to a temperature of about 35 to C. to produce the 2-sulfo-2-alkylcarboxy1ic acid.

15. The process of claim 14 wherein the Z-alkylcarboxylic acid is 2-methyleicosanoic acid and the product is 2-sulfo-2-methyleicosanoic acid.

16. The process of claim 14 wherein the 2-alkylcarboxylic acid is Z-methyloctadecanoic acid and the product is 2-su1fo-2-methyloctadecanoic acid.

17. The process of claim 14 wherein the 2-a1kylcarboxylic acid is Z-butyltetradecanoic acid and the product is 2-sulfo-Z-butyltetradecanoic acid.

18. The process of claim 14 wherein the 2-alkylcarboxylic acid is Z-heptylundecanoic acid and the product is 2-sulfo-Z-heptylundecanoic acid.

19. The process of claim 14 wherein the 2-alkylcarboxylic acid is 2-octyldecanoic acid and the product is 2-sulfo-2-octy1decanoic acid.

References Cited UNITED STATES PATENTS 11/1938 Suter 260400 X OTHER REFERENCES NICHOLAS S. RIZZO, Primary Examiner. J. H. TTJRNIPSEED, Assistant Examiner. 

